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In chlorobezene each carbon atom is sp² Hybridised due to resonance there is a partial double bond character,so bond length is short.

1. In t-butyl chloride, there is niore steric hindrance and it involves formation of a stable tertiary carbocation. Therefore it reacts with KOH by S_N1 mechanism rather than S_N2 mechanism because S_N1 mechanism is faourable in case of steric crowding and is directly proportional to partial positive charge on carbon atom. In n-butyl chloride, there is least steric hindrance and involves formation of less stable primary carbocation. Thus it takes place in one step and is favoured by S_N² mechanism.

2. Melting point of p – dichiorobenzene is higher than that of ortho and meta-dichiorobenzene. This is due to the fact that is has a symmetrical structure and therefore, its molecules can easily pack closely in the crystal lattice. p-dichlorobcnzene being more symmetrical fits closely in the crystal lattice and has stronger intermolecular attraction than o & m isomers. So p-isomer has high melting point than the corresponding o & m-isomers

When 2-bromobutane react with alcoholic KOH, the products formed are 1-butene & 2-butene.

The product formed when tertiary butyl chloride is treated with alcoholic KOH is Iso-butylene .

(b) E₁ mechanism

When chloroform is treated with primary amine and KOH, we get Offensive odours.

(b) Carbyianiine test

Iodination reactions are reversible in nature. To carry out the reaction in the forward direction, HI formed during iodination is removed by oxidation. HIO₄ is used as an oxidising agent.

(v) Assertion and reason both are correct statements but reason is not correct explanation of assertion.

1. is because the nucleophile attaches itself on the side opposite to the one where the halogen atom is present.

2. Equimolar mixture of ‘d’ and T forms of an optically active compound is called racemic mixture.

3. Racemic mixture is optically inactive due to external compensation. A mixture containing two enantiomers in equal proportions will have zero optical rotation, as the rotation due to one isomer will be cancelled by the rotation due to the other isomer.

On heatrng CHCl₃ with aqueous NaOH solution, the product formed is HCOONa.

CH₃ - CH₂ - Br would undergo S_N² reaction faster it has less steric hindrance than tert - butyl bromide.

CH₃-CH₂-Br

Because it is a primary halide / (1°) halide.

(a) because neem powder will not harm soil. 

(b) Ravi Prasad. 

(c) Application of scientific knowledge. Environmental concern. 

The product obtained in fittig reaction of chlorobenzene is Biphenyl.

(a) 1 -chloro-4-nitrobenzene

BrCH=CH-CHCH₂CI

1. The IUPAC name of the insecticide DDT is, p-dichloro-diphenyl trichioroethane. 

2. Even DDT is an effective insecticide. Now-adays it is banned because of its long term toxic effects. 

3. DDT is very persistent in the environment and it has a high affinity for fatty tissues. As a result, DDT gets accumulated in animal tissue fat, in particular that of birds of prey with subsequent thinning of their eggs shells and impacting their rate of reproduction. That is why DDT is banned in most of the countries.

• DDT is used lo control certain insects which carries diseases like malaria and yellow fever. 
• It is used in farms to control some agricultural pests. 
• It is used in building construction as pest control agent. 
• It is used to kill certain kind of insects like housefly and mosquitoes due to its high and specific toxicity.

(a) Both assertion and reason are true and reason is the correct explanation of assertion.

Ethyl bromide reacts with alcoholic KNO₂ to form Ethyl nitrite.

Ethyl bromide reacts with alcoholic AgCN to form CH₃CH₂NC.

(a) Halo alkanes have higher boiling point than the parent alkane with same number of carbons because of strong inter molecular forces of attraction.

• 2-bromobutane is optically active and it undergoes S_N1 reaction with aqueous KOH.
• The product obtained will be an optically inactive racemic mixture. 
• As nucleophilic reagent OH^- ion can attack the carbocation from both sides to form equal proportions of dextro and levo rotatory optically active isomers, it results in the formation of optically inactive racemic mixture

Haloalkanes reacts with aqueous solution of KOH to form Alcohol.

Ethyl alcohol is first treated with sodium to form sodium ethoxide C₂H₅OH + Na C₂H₅O– Na⁺ + H₂ 

Sodium ethoxide is then treated with ethyl halide to form di ethyl ether. 

SN² C₂H₅O Na + — C₂H₅X → C₂H₅O C₂H₅ + NaX (Williamson synthesis)  

carbonyl chloride/phosgene

(iii) 1-Bromo-2-methylbutane

(iv) (CH₃)₃C—I

(B) Undergoes S_N1 reaction faster than (A) because in case of (B), the carbocation formed after the loss of Cl ^– is stabilised by resonance, whereas, no such stabilisation is possible in the carbocation obtained from (A).

Solution

C₆H₅—CH₂—Cl

In the Gattermann reaction of preparation of chiorobenzene from benzene, the catalyst used is Cu / HCl.

Conversion of benzene to chiorobenzene in the presence of CuCl₂ / HCl is named as Gattermann reaction.

The hybridised state of carbon in haloarenes is sp².

Primary alkyl halide react with aqueous NaOH follows S_N2.

(a) Both (A) and (R) are correct and (R) is the correct explanation of (A).

1. CH₃I will react faster because C-I bond undergoes cleavage more easily as compared to C-Br bond.

2. CH₃CI will react faster because in it the carbon carrying halogen is sterically less hindered.

CH₃ will react faster in S_N² reaction because CH₃I has a better levaving group than CH₃ Br.

Ethyl-methyl ether ethene is obtained by the action of methyl magnesium iodide with Chioro-aimethyl-ether.

• CH₃I will react faster because C-I bond undergoes cleavage more easily as compared to C-Br bond.
• CH₃CI will react faster because in it the carbon carrying halogen is sterically less hindered.

• Chlorination of methane is a free radical substitution reaction. 
• Before chlorine reacts with methane, the Cl-Cl single bond must break to form free radicals and this can only be done in the presence of ultraviolet light.
• In dark, chlorine free radicals formation is not possible and so chlorination of methane is not possible in dark. 
• The ultraviolet light is a source of energy and it being used to break of Cl-Cl and produce Cl free radical Free radical’s which can attack methane. in dark this is not possible.

1. Since I^- ion a better leaving group than Br^- ion, therefore CH₃I will react faster than CH₃Br in S_N2 reaction with OH^- ion. 

2. On steric grounds 1° alkyl halides are more reactive than tert alkyl halide in S_N2 reactions. Therefore, CH₃Cl will react at a faster rate than (CH₃)₃ CCl in a S_N2 reaction with OH^- ion.

Williamson’s synthesis: 

Haloalkanes when boiled with sodium alkoxide gives the corresponding ether.

CH₃ - CH₂Br(Bromo ethane) + CH₃CH₂ONa (Sodium ethoxide) \(\longrightarrow\)CH₃ - CH₂ - O - CH₂ - CH₃(Diethyl ether) + NABr

(a) Williamson’s synthesis of ether is an example of nucleophilic substitution reaction.

1. Because in ethyl iodide, iodide being the best leaving group among all the halide ions. Rate of S_N2 reaction ability of leaving group.

2. (±) 2-hutanol is a racemic mixture which is optically inactive due to the external compensation. 

3. Due to resonance in halobenzene, it has a smaller bond length value as compared to CH₃ - X.

• Chloroform is used as a solvent in pharmaceutical industry. 
• It is used for producing pesticides and drugs. 
• It is used as an anaesthetic.

Correct answer is (a) CH₃CHCl₂

(a) Chiorobenzene

Some haloalkanes when treated with alcoholic KOH yield a mixture of olefins with different amounts. It is explained by Saytzeff’s rule which states that in a dehydrohalogenation reaction, the preferreed product is that alkene which has more number ofalkyl group attached to the doubly bonded carbon atom.